1. Field of the Invention
The present invention relates to an optical encoder including a stationary slit part.
2. Description of the Related Art
An optical encoder is used to detect information on a position, velocity and acceleration or the like of a rotatable object in rotational motion. The information detected by the optical encoder is used to control a servo motor provided at a drive shaft of a machine tool, for example.
The optical encoder includes a stationary slit part and a rotational slit part which allow part of light emitted from a light source to pass therethrough. JP-A-2005-274479 discloses a known optical encoder.
Referring to FIGS. 13A and 13B, a configuration of a stationary slit part 200 according to the related art is described. The stationary slit part 200 includes a plate-like main body 204, and is made of glass or metal. A central portion of the main body 204 is formed with a patterned portion 202 which includes a plurality of slits arranged according to a predetermined pattern.
The stationary slit part 200 also includes fixed portions 206 on opposite edges of the main body 204. The fixed portions 206 of the stationary slit part 200 are fixed to a base 210 by an adhesive 212, as shown in FIG. 13B.
However, since the stationary slit part 200 and the base 210 are often made of different materials, when temperature changes, an adhered surface between the stationary slit part 200 and the base 210 is shifted due to a difference in coefficients of thermal expansion, and therefore the fixing strength therebetween may be decreased. Possibly, the stationary slit part 200 may slide off the base 210.
Accordingly, there is a need for an optical encoder including a stationary slit part with improved reliability.